Gun violence has become a widely publicized issue in recent years. According to recent statistics, one in three people in the United States knows someone who has been shot. On average, 31 Americans are murdered with guns every day and 151 are treated for a gun assault in an emergency room. In 2015 alone, more than 12,000 people were killed in the United States by a gun, and many others were injured. Gun violence has unfortunately occurred in a variety of public places, such as schools, places of worship, sporting event venues, nightclubs, and airports. While the use of metal detectors and other security measures are frequently employed in an attempt to prevent firearms in such venues, incidents of gun violence in public continue to be a major issue.
Gunshot detection by electronic devices, rather than by humans, is performed for a variety of purposes and applications that include the military, law enforcement, security, and public safety. Gunshot detection is a complex task because of the sheer variety of weapons and explosive devices that can produce the gunshot event. Identifying the point of origin of the gunshot is critical to identifying and tracking a suspected shooter. The identification of the source of the gunshot is complicated by many factors including the spatial environment in which the gunshot event occurs. Gunshot detection and shooter identification are critical elements in many military, law enforcement, security, and public safety scenarios.
Some early work in detecting gunshots in an outdoor setting involved several microphones spread out over a large distance. A gunshot is often so loud it can be heard many thousands of feet away in an outdoor setting. The occurrence of a gunshot would then register on the microphones, but at slightly different times. Because the speed of sound in dry air at sea level at 68° Fahrenheit is about 1125 feet/second, a gunshot somewhere between two microphones that are 2500 feet apart would be detected at the microphones one or even two seconds apart, which is an easily detectable difference. Furthermore, the relative times of detection are an indication of the proximity of the gunshot to one microphone versus another microphone. Unfortunately, this scheme cannot distinguish between gunshots and other similar explosive sounds, such as car backfires, construction noises, fireworks, etc.
The problem of gunshot detection indoors is many times more complicated than gunshot detection outdoors. In indoor settings, many complicating factors intrude upon accurate gunshot detection. For example, in an indoor setting, the probability of extensive sound reverberations and echoes from the initial gunshot is very high. In addition, rooms within the indoor setting often have convoluted acoustic pathways. These acoustic pathways are often blocked by closed doors, which cause many decibels of sound attenuation. Furthermore, indoor settings are often spread over multiple floors and replete with crowds of people, which makes dealing with indoor gunshots extremely challenging for law enforcement officers or other public safety personnel. Additionally, many other distracting sonic and visual interferences may be present in a crowded, indoor environment, including screams, flashlights, police alarms, building alarms, fire alarms, earthquake alarms, tornado alarms, and the like. Gunshot detection in an indoor environment is an important element of public safety.